Valve timing adjuster

ABSTRACT

A control apparatus controls supply of working fluid to advancing chambers and retarding chambers. The control apparatus alternately and repeatedly implements an advancing supply period, during which the working fluid is supplied to the advancing chambers, and a retarding supply period, during which the working fluid is supplied to the retarding chambers, at time of limiting a phase of a camshaft relative to a crankshaft within a target phase range.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by referenceJapanese Patent Application No. 2007-188730 filed on Jul. 19, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a valve timing adjuster, which adjustsopening and closing timing (hereinafter, simply referred to as valvetiming) of at least one of an intake valve and an exhaust valve of aninternal combustion engine.

2. Description of Related Art

For example, a previously known valve timing adjuster includes a housingand a vane rotor. The housing serves as a first rotatable body and isrotated together with a drive shaft, and the vane rotor serves as asecond rotatable body and is rotated together with a driven shaft. Inthe valve timing adjuster, advancing chambers and retarding chambers arearranged one after another in the rotational direction. Each of theadvancing chambers and the retarding chambers is formed between acorresponding one of shoes of the housing and a corresponding one ofvanes of the vane rotor. Working fluid is supplied to the advancingchambers or the retarding chambers to drive the driven shaft relative tothe drive shaft in an advancing direction or a retarding direction toadjust the valve timing.

In such a valve timing adjuster, as recited in, for example, JapaneseUnexamined Patent Publication No. 2006-63835, a variable torque isapplied to the driven shaft in response to the rotation of the internalcombustion engine. The variable torque is a torque that periodicallyvaries, i.e., changes in an advancing direction for advancing the drivenshaft or in a retarding direction for retarding the driven shaft inresponse to the rotation of the internal combustion engine. Here, thevariable torque is caused by, for example, a spring reaction force ofeach corresponding valve, which is opened and closed by the drivenshaft. Also, in a case where a mechanical pump is driven by the drivenshaft, the variable torque is generated by a drive reaction force of themechanical pump. In the valve timing adjuster, in which the variabletorque is transmitted through the driven shaft, the phase of the drivenshaft (hereinafter, referred to as an engine phase) relative to thedrive shaft is set when the torques applied to the driven shaft arebalanced. Besides the above-described variable torque, these torquesalso include a rotational torque, which is generated by supply of thefluid to the advancing chambers and the retarding chambers, and anurging torque, which is generated in a case where a spring is providedto urge the driven shaft.

When a solenoid spool valve, which is used to control the supply of thefluid to the advancing chambers and the retarding chambers, iscontrolled in the manner described in Japanese Unexamined PatentPublication No. 2006-63835, the engine phase can be limited within atarget phase range to substantially hold the valve timing. Here, when anaverage value (average torque) of the variable torque is balanced withthe other torque (e.g., the urging torque) or becomes substantially zero(for example, in a case where a bearing friction of the driven shaft issubstantially zero), the supply of the fluid to both of the advancingchambers and the retarding chambers from the solenoid spool valve may bestopped to make the rotational torque applied to the driven shaft tozero. In this way, the engine phase can be limited within the targetphase range. However, in such a case, when the variable torque reaches,for example, its peak torque and thereby becomes large, the advancingchambers or the retarding chambers may possibly be compressed to causeoutflow of the working fluid from the advancing chambers or theretarding chambers. This may possibly cause fluctuating movement(repeated forward and backward rotation often referred to as oscillatingrotational movement) of the vane rotor relative to the housing. Thiskind of the fluctuating movement may make it difficult to keep theengine phase within the target phase range for appropriately adjustingthe valve timing, which is appropriate for the internal combustionengine. Also, it may cause generation of the hammering sound, whichwould be generated by hitting movement of the vane rotor against thehousing. Thus, such fluctuating movement is not desirable.

SUMMARY OF THE INVENTION

The present invention addresses the above disadvantages. Thus, it is anobjective of the present invention to provide a valve timing adjuster,which enables adjustment of valve timing in a more appropriate mannerfor an internal combustion engine, and which limits generation ofhammering sound.

To achieve the objective of the present invention, there is provided avalve timing adjuster that adjusts opening and closing timing of atleast one of an intake valve and an exhaust valve of an internalcombustion engine and is placed in a drive force transmission system,which transmits a drive force from a drive shaft of the internalcombustion engine to a driven shaft that drives the at least one of theintake valve and the exhaust valve to open and close the same. The valvetiming adjuster includes a first rotatable body, a second rotatable bodyand a supply control means. The first rotatable body is rotated togetherwith the drive shaft. The second rotatable body is rotated together withthe driven shaft. The second rotatable body cooperates with the firstrotatable body to form an advancing chamber and a retarding chamber,which are arranged one after another in a rotational direction betweenthe first rotatable body and the second rotatable body, and the secondrotatable body drives the driven shaft in an advancing direction or aretarding direction relative to the drive shaft upon supplying ofworking fluid to the advancing chamber or the retarding chamber. Thesupply control means is for controlling supply of the working fluid tothe advancing chamber and the retarding chamber. The supply controlmeans alternately and repeatedly implements an advancing supply period,during which the working fluid is supplied to the advancing chamber, anda retarding supply period, during which the working fluid is supplied tothe retarding chamber, at time of limiting a phase of the driven shaftrelative to the drive shaft within a target phase range.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features andadvantages thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings in which:

FIG. 1 is a schematic diagram showing a structure of a valve timingadjuster having a drive apparatus viewed along line I-I in FIG. 2according to a first embodiment of the present invention:

FIG. 2 is a cross sectional view taken along line II-II in FIG. 1;

FIG. 3 is a lateral view of the drive apparatus shown in FIG. 1;

FIG. 4 is a schematic descriptive diagram for describing an operation ofa control apparatus of the valve timing adjuster shown in FIG. 1;

FIG. 5 is a schematic descriptive diagram for describing an operation ofthe control apparatus shown in FIG. 1;

FIG. 6 is another schematic descriptive diagram for describing anoperation of the control apparatus shown in FIG. 1;

FIG. 7 is a schematic descriptive diagram for describing a variabletorque applied to the drive apparatus shown in FIG. 1;

FIG. 8 is a diagram for describing an average variable torque applied tothe drive apparatus of FIG. 1 and an urging torque generated in thedrive apparatus;

FIGS. 9A to 9C are diagrams for describing characteristics of the valvetiming adjuster of FIG. 1;

FIGS. 10A to 10C are diagrams for describing the characteristics of thevalve timing adjuster of FIG. 1;

FIGS. 11A to 11C are diagrams for describing the characteristics of thevalve timing adjuster of FIG. 1;

FIG. 12 is a diagram for describing characteristics of a valve timingadjuster according to a second embodiment of the present invention;

FIG. 13 is a diagram for describing characteristics of a valve timingadjuster according to a third embodiment of the present invention;

FIG. 14 is a diagram for describing the characteristics of the valvetiming adjuster according to the third embodiment; and

FIGS. 15A and 15B are diagrams for describing characteristics of a valvetiming adjuster according to a fourth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described with reference tothe accompanying drawings. In the following respective embodiments,similar components will be indicated by the same reference numerals.

First Embodiment

FIGS. 1 to 3 show a valve timing adjuster 1 of a first embodiment of thepresent invention implemented in an internal combustion engine of avehicle. The valve timing adjuster 1 is of a hydraulically controlledtype, which uses hydraulic oil as working fluid and which adjusts thevalve timing of exhaust valves. The valve timing adjuster 1 includes adrive apparatus 10 and a control apparatus 30. The drive apparatus 10 ishydraulically driven in a drive force transmission system, whichtransmits a drive force of an undepicted crankshaft (serving as a driveshaft) of the internal combustion engine to a camshaft 2 (serving as adriven shaft) of the internal combustion engine. The control apparatus30 serves as a supply control means and controls supply of oil to thedrive apparatus 10. A mechanical fuel injection pump (not shown) of theinternal combustion engine is connected to the camshaft 2, which drivesthe exhaust valves to open and close the same. The fuel injection pumpis driven in response to the rotation of the camshaft 2.

First, the drive apparatus 10 will be described. A housing (serving as afirst rotatable body) 18 of the drive apparatus 10 includes a sprocket11, a shoe housing 12 and a front plate 13.

The shoe housing 12 is configured into a cylindrical body and includes aplurality of shoes 12 a-12 d, which are placed at generally equalintervals in the rotational direction. Each shoe 12 a-12 d projectsradially inward and serves as a partition. A projecting end surface ofeach shoe 12 a-12 d forms an arcuate surface when it is viewed in adirection perpendicular to the plane of FIG. 2. The projecting endsurface of each shoe 12 a-12 d slidably engages an outer peripheral wallsurface of a boss 14 a of a vane rotor 14. A seal member 15 is fittedinto a recess, which is provided in the projecting end surface of eachshoe 12 a-12 d. A receiving chamber 50 is formed between each adjacenttwo of the shoes 12 a-12 d, which are adjacent to each other in therotational direction. Each receiving chamber 50 is defined by lateralsurfaces of the corresponding shoes 12 a-12 d and an inner peripheralwall surface of the shoe housing 12 and has a fan shape as viewed in thedirection perpendicular to the plane of FIG. 2.

The sprocket 11 is configured into a cylindrical tubular body, and thefront plate 13 is configured into an annular plate body. The shoehousing 12 is coaxially clamped between the sprocket 11 and the frontplate 13, and the sprocket 11, the shoe housing 12 and the front plate13 are fixed together with bolts. The sprocket 11 is connected to thecrankshaft through a timing chain (not shown). In this way, the housing18 is rotated together with the crankshaft when the drive force istransmitted from the crankshaft to the sprocket 11 upon the operation ofthe internal combustion engine. At this time, the housing 18 is rotatedin a clockwise direction in FIGS. 2 and 3.

The vane rotor 14, which serves as a second rotatable body, is receivedin the housing 18. Two opposed axial end surfaces of the vane rotor 14are slidably engaged with an inner surface of the sprocket 11 and aninner surface of the front plate 13, respectively. The vane rotor 14includes the cylindrical boss 14 a and a plurality of vanes 14 b-14 e.

A cylindrical tubular bush 20 is relatively rotatably received at alocation radially inward of the front plate 13 and is coaxially engagedwith one end portion of the boss 14 a. The boss 14 a is fixed togetherwith the bush 20 to the camshaft 2, which is coaxial with the boss 14 a,with a bolt. Thus, the vane rotor 14 is rotated together with thecamshaft 2 and the bush 20 in the clockwise direction in FIGS. 2 and 3.Furthermore, the vane rotor 14 and the camshaft 2 are rotatable relativeto the housing 18. In FIGS. 2 and 3, a direction of an arrow X indicatesan advancing direction (a direction toward an advancing side) of thevane rotor 14 relative to the housing 18, and a direction of an arrow Yindicates a retarding direction (a direction toward a retarding side) ofthe vane rotor 14 relative to the housing 18.

An assist spring 22 is a torsion coil spring and serves as a resilientmember. The assist spring 22 is placed radially inward of the bush 20.One end portion of the assist spring 22 is anchored to the housing 18through an anchoring pin 18 a, and the other end portion of the assistspring 22 is anchored to an anchoring groove 14 f, which is formed inthe boss 14 a of the vane rotor 14. A restoring force, which isgenerated by the assist spring 22, serves as an urging torque Ts thaturges the vane rotor 14 in the advancing direction X relative to thehousing 18.

The vanes 14 b-14 e, which are placed one after another at the generallyequal intervals in the rotational direction at the boss 14 a, radiallyoutwardly project from the boss 14 a and are received in the receivingchambers 50, respectively. A projecting end surface of each vane 14 b-14e forms an arcuate surface as viewed in the direction perpendicular tothe plane of FIG. 2 and is slidably engaged with the inner peripheralwall surface of the shoe housing 12. A seal member 16 is fitted into arecess, which is provided in the projecting end surface of each vane 14b-14 e.

Each vane 14 b-14 e divides the corresponding receiving chamber 50 toform an advancing chamber and a retarding chamber relative to thehousing 18. Specifically, the advancing chamber 51 is formed between theshoe 12 a and the vane 14 b, and the advancing chamber 52 is formedbetween the shoe 12 b and the vane 14 c. Furthermore, the advancingchamber 53 is formed between the shoe 12 c and the vane 14 d, and theadvancing chamber 54 is formed between the shoe 12 d and the vane 14 e.Also, the retarding chamber 55 is formed between the shoe 12 d and thevane 14 b, and the retarding chamber 56 is formed between the shoe 12 aand the vane 14 c. Also, the retarding chamber 57 is formed between theshoe 12 b and the vane 14 d, and the retarding chamber 58 is formedbetween the shoe 12 c and the vane 14 c.

Therefore, when the vane rotor 14 is placed in a most advanced positionin the advancing direction X with respect to the housing 18, a volume ofeach advancing chamber 51-54 is maximized while a volume of eachretarding chamber 55-58 is minimized. In contrast, when the vane rotor14 is placed in a most retarded position in the retarding direction Ywith respect to the housing 18, the volume of each retarding chamber55-58 is maximized while the volume of each advancing chamber 51-54 isminimized.

The advancing chambers 51-54 are communicated with advancing passages61-64, which are formed in the sprocket 11 and are communicated with anadvancing passage 71 formed in the camshaft 2. The retarding chambers55-58 are communicated with retarding passages 65-68, which are formedin the vane rotor 14, and the retarding passages 65-68 are communicatedwith a retarding passage 72 formed in the camshaft 2.

A stopper pin 26 is received in the vane 14 b. When the stopper pin 26is urged by the restoring force of a compression coil spring 28 and isthereby fitted into an engaging ring 27 of the sprocket 11, the vanerotor 14 is arrested in the most advanced position, which is mostadvanced in the advancing direction X relative to the housing 18. Whenthe stopper pin 26 receives the pressure of the oil supplied from theretarding chamber 55 through a passage 29 formed in the sprocket 11, thestopper pin 26 is axially displaced from the engaging ring 27.Therefore, the rotation of the vane rotor 14 relative to the housing 18is enabled, i.e., is permitted.

Next, the control apparatus 30 will be described. In the controlapparatus 30, the advancing passage 73 and the retarding passage 74 arecommunicated with the advancing passage 71 and the retarding passage 72,respectively, of the camshaft 2.

A switch control valve 31 is communicated with the advancing passage 73,the retarding passage 74, a pump passage 75 and drain passages 76, 77.An oil pump (serving as a fluid supply source) 4 is provided in the pumppassage 75. The oil pump 4 draws the oil from the oil tank 5 through anupstream side part of the pump passage 75 and discharges the oil towardthe switch control valve 31 through a downstream side part of the pumppassage 75. The oil pump 4 of the present embodiment is a mechanicalpump that is driven by the crankshaft. The drain passages 76, 77 areprovided to enable draining of the oil from the switch control valve 31toward the oil tank 5.

The switch control valve 31 is a solenoid spool valve that axiallydrives the spool 34 in response to a balance between the drive force,which is generated by a solenoid drive arrangement 32 upon energizationthereof and a restoring force, which is generated by the return spring33 in a direction opposite from the direction of the drive force. Theswitch control valve 31, which is connected with the passages 73-77,switches the communication of the pump passage 75 and the drain passages76, 77 to the advancing passage 73 and the retarding passage 74.

Specifically, when the drive current, which is supplied to the solenoiddrive arrangement 32, is smaller than a reference value Ib, theadvancing passage 73 is communicated with the pump passage 75, so thatthe oil discharged from the oil pump 4 is supplied to the advancingpassage 73 through the pump passage 75, as shown in FIG. 4. At thistime, as shown in FIG. 4, the retarding passage 74 is communicated withthe drain passage 76, and the oil of the retarding passage 74 is drainedto the oil tank 5 through the drain passage 76.

When the drive current, which is supplied to the solenoid drivearrangement 32, is larger than the reference value Ib, the retardingpassage 74 is communicated with the pump passage 75, so that the oildischarged from the oil pump 4 is supplied to the retarding passage 74through the pump passage 75, as shown in FIG. 5. At this time, as shownin FIG. 5, the advancing passage 73 is communicated with the drainpassage 77, and the oil of the advancing passage 73 is drained to theoil tank 5 through the drain passage 77.

When the drive current, which is supplied to the solenoid drivearrangement 32, is equal to the reference value Ib, the communication ofeach of the advancing passage 73 and the retarding passage 74 to thepump passage 75 and the drain passages 76, 77 is interrupted, as shownin FIG. 6. Therefore, the oil, which is discharged from the oil pump 4,is not supplied to the advancing passage 73 and the retarding passage74, and the oil in the advancing passage 73 and the oil in the retardingpassage 74 remain therein.

A control circuit 36 of the control apparatus 30 shown in FIG. 1includes a microcomputer, which has a memory 36 a. The control circuit36 controls electric power supply to the switch control valve 31 andalso controls the operation of the internal combustion engine.Specifically, besides the switch control valve 31, a plurality ofsensors, which includes a cam angle sensor 7 and a crank angle sensor 8,is electrically connected to the control circuit 36. The control circuit36 computes an actual phase and a target phase of the camshaft 2relative to the crankshaft based on an output of each correspondingsensor. Based on the computed result, the control circuit 36 controlsthe power supply to the switch control valve 31, i.e., controls thedrive current supplied to the switch control valve 31. The cam anglesensor 7 is placed, for example, adjacent to the camshaft 2 to sense arotational angle of the camshaft 2. The crank angle sensor 8 is placed,for example, adjacent to the crankshaft and senses a rotational angle ofthe crankshaft.

The drive apparatus 10 and the control apparatus 30 of the valve timingadjuster have been described. Now, the variable torque, which is appliedto the drive apparatus 10, will be described.

During the operation of the internal combustion engine, the variabletorque (i.e., the torque that varies with time, more specifically,oscillates with time) is applied to the camshaft 2 and the vane rotor 14in response to a spring reaction force from each corresponding exhaustvalve driven to open and close by the camshaft 2 and the drive reactionforce of the fuel injection pump, which is driven by the camshaft 2.Here, as shown in FIG. 7, the variable torque periodically changesbetween a positive torque, which acts in a direction for retarding theengine phase of the camshaft 2 relative to the crankshaft, and anegative torque, which acts in a direction for advancing the enginephase. In FIG. 7 as well as other drawings, the retarding is abbreviatedas “RTD”, and the advancing is abbreviated as “ADV”. The variable torqueof the present invention is such that a peak torque Tc+ of the positivetorque is larger than a peak torque Tc− of the negative torque due tothe friction between the camshaft 2 and a journal (not shown) forsupporting the camshaft 2. Therefore, an average torque (hereinafter;referred to as an average variable torque) Tca of the variable torque isbiased on the positive torque side, which is opposite from the urgingtorque Ts of the assist spring 22, i.e., on the retarding side Y.Furthermore, as shown in FIG. 8, when the rotational speed (i.e., thenumber of revolutions per unit time) of the internal combustion engineis increased, the average torque Tca is increased.

Now, the variable torque, which is applied to the drive apparatus 10,will be described. Hereinafter, the characteristic operation of thevalve timing adjuster 1 will be described.

In a stop state of the internal combustion engine, the stopper pin 26 isfitted into the engaging ring 27 by the restoring force of thecompression coil spring 28. When the internal combustion engine isstarted from the stop state, the oil pump 4 is driven, and the retardingpassage 74 is communicated with the pump passage 75 by controlling thedrive current, which is applied from the control circuit 36 to theswitch control valve 31, to a value that is larger than the referencevalue Ib. Then, the oil, which is discharged from the oil pump 4, issupplied to the respective retarding chambers 55-58 through the pumppassage 75 and the retarding passages 74, 72, 65-68. Therefore, thestopper pin 26 receives the oil pressure from the retarding chamber 55through the passage 29, so that the stopper pin 26 is removed, i.e., isdislodged from the engaging ring 27 against the restoring force of thecompression coil spring 28 upon increasing the oil pressure, which isreceived from the retarding chamber 55, to the predetermined value.Therefore, the vane rotor 14 is placed into the rotatable state wherethe vane rotor 14 is rotatable relative to the housing 18.

Thereafter, the control circuit 36 controls the electric power supply tothe switch control valve 31 to change each communicating one of the pumppassage 75 and the drain passages 76, 77, which is communicated with thecorresponding one of the advancing passage 73 and the retarding passage74, thereby adjusting the valve timing. Now, the valve timing controloperation will be described in detail.

First, the valve timing advancing operation for advancing the valvetiming will be described. In the case where the accelerator of theinternal combustion engine is in an off state or in the case where apredetermined operational condition, which indicates a low/middle speedhigh load operational state of the internal combustion engine thatrequires the output torque, is satisfied, the control circuit 36controls the drive current supplied to the switch control valve 31 to avalue smaller than the reference value Ib. In this way, the advancingpassage 73 is communicated with the pump passage 75, and the retardingpassage 74 is communicated with the drain passage 76. Therefore, the oildischarged from the oil pump 4 is supplied to the respective advancingchambers 51-54 through the pump passage 75 and the advancing passages73, 71, 61-64. Furthermore, at this time, the oil in the respectiveretarding chambers 55-58 is drained to the oil tank 5 through theretarding passages 65-68, 72, 74 and the drain passage 76. In this way,the pressure of the oil is applied to the vanes 14 b-14 e, which facethe advancing chambers 51-54, respectively, thereby generating therotational torque Tv, which drives the vane rotor 14 to rotate the samerelative to the housing 18 in the advancing direction X. As a result,the engine phase of the camshaft 2 relative to the crankshaft andthereby the valve timing is advanced.

Next, the valve timing retarding operation for retarding the valvetiming will be described. In the case where a predetermined operationalcondition, which indicates a normal operational state where the internalcombustion engine is driven with a light load, is satisfied, the controlcircuit 36 controls the drive current supplied to the switch controlvalve 31 to a value larger than the reference value Ib. Thereby, theretarding passage 74 is communicated with the pump passage 75, and theadvancing passage 73 is communicated with the drain passage 77. Thus,the oil, which is discharged from the oil pump 4, is supplied to therespective retarding chambers 55-58 through the pump passage 75 and theretarding passages 74, 72, 65-68. Furthermore, at this time, the oil inthe respective advancing chambers 51-54 is drained to the oil tank 5through the advancing passages 61-64, 71, 73 and the drain passage 77.In this way, the pressure of the oil is applied to the vanes 14 b-14 e,which face the retarding chambers 55-58, respectively, therebygenerating the rotational torque Tv, which drives the vane rotor 14 torotate the same relative to the housing 18 in the retarding direction Y.As a result, the engine phase of the camshaft 2 relative to thecrankshaft and thereby the valve timing is retarded.

Next, the valve timing holding operation for substantially holding thevalve timing will be described. In the case where a predeterminedoperational condition (hereinafter, a stable operational condition),which indicates a stable operational state (e.g., a holding state of theaccelerator or accelerator pedal) of the internal combustion engine, issatisfied as a limiting condition, the control circuit 36 controls thedrive current supplied to the switch control valve 31 to supply the oilto the respective advancing chambers 51-54 like in the case of theadvancing operation described above. Thereby, the rotational torque Tvin the advancing direction X against the average variable torque Tca isgenerated. At this time, the control circuit 36 computes an actual phasePr based on the output of the cam angle sensor 7 and the output of thecrank angle sensor 8 with respect to the engine phase of the camshaft 2relative to the crankshaft. Thereby, the control circuit 36 adjusts thedrive current supplied to the switch control valve 31 within a rangelower than the reference value Ib to limit the actual phase Pr within apredetermined target phase range ΔPt. Therefore, the current valvetiming is substantially held.

When the valve timing is substantially held in the above describedmanner, the average variable torque Tca may possibly be balanced withthe urging torque Ts of the assist spring 22, as indicated with a shadedcircle in FIG. 8. Therefore, in such a case, even when the drive currentsupplied to the switch control valve 31 is adjusted, this adjustment ismade within the range lower than the reference value Ib. Thereby, thesupply of the oil to the respective advancing chambers 51, 54 ismaintained. As a result, the actual phase Pr reaches an advancing end ofthe target phase range Apt, which is opposite from a bias of the averagevariable torque Tc. Thus, in this case, similar to the above case ofretarding operation, the control circuit 36 controls the drive currentsupplied to the switch control valve 31 to supply the oil to therespective retarding chambers 55, 58 to return the actual phase Pr to anintermediate phase (a phase intermediate between the advancing end andthe retarding end) within the target phase range ΔPt, and thereafter thecontrol circuit 36 executes an alternately repeating supply operation.

Specifically, in the alternately repeating supply operation, asindicated in FIGS. 9B, 10B and 11B, an advancing (ADV) supply period anda retarding (RTD) supply period are alternately repeatedly implemented.In the advancing supply period (also referred to as an advancing supplyprocess), the oil is supplied to the respective advancing chambers 51-54by controlling the drive current supplied to the switch control valve 31in the manner similar to that of the advancing operation discussedabove. In the retarding supply period (also referred to as a retardingsupply period), the oil is supplied to the respective retarding chambers55-58 by controlling the drive current supplied to the switch controlvalve 31 in the manner similar to that of the retarding operationdiscussed above. At this time, the actual phase Pr is limited within thetarget phase range ΔPt, so that the holding of the valve timing ismaintained.

Here, in the alternately repeating supply operation of the presentembodiment, the supply of the oil to the respective advancing chambers51-54 is maintained throughout each corresponding advancing supplyperiod, and the supply of the oil to the respective retarding chambers55-58 is maintained throughout each corresponding retarding supplyperiod. Furthermore, in the alternately repeating supply operation, theperiod ω of cycle of the change in the variable torque, whichcorresponds to the current actual rotational speed Nr of the internalcombustion engine, is computed based on the correlation information,which indicates the relationship between the rotational speed of theinternal combustion engine and the period ω of cycle of the change inthe variable torque (see FIG. 7). Then, the advancing supply period andthe retarding supply period are alternately repeated in a manner thatcauses generation of the rotational torque Tv, which shows the cyclicchange having the period of cycle that is different from the computedperiod ω of cycle of the change in the variable torque, as shown inFIGS. 9A, 9C, 10A, 10C, 11A and 11C. At this time, as long as the actualphase Pr does not exceed the target phase range ΔPt, the period of cycleof the change in the rotational torque Tv may be shorter than the periodω of cycle of the change in the variable torque, as shown in FIG. 9C, ormay be longer than the period ω of cycle of the change in the variabletorque, as shown in FIG. 10C, or may be the same as the period ω ofcycle of the change in the variable torque with the reversed phase(advanced or retarded), as shown in FIG. 11C.

The correlation information, which indicates the relationship betweenthe rotational speed of the internal combustion engine and the period ωof cycle of the change in the variable torque, is preset in a form of amap, a table or a mathematical equation according to the specificationof the internal combustion engine installed in the vehicle together withthe valve timing adjuster 1. The correlation information is stored inthe memory 36 a of the control circuit 36 and is used to compute theperiod ω of cycle of the change in the variable torque. Alternatively,the period ω of cycle of the change in the variable torque may belearned from the output of the cam angle sensor 7 and the output of thecrank angle sensor 8, and the correlation information stored in thememory 36 a may be updated regularly based on the result of thelearning.

Furthermore, the holding operation is continued until the stableoperational condition, which serves as the limiting condition, is nolonger satisfied.

As described above, even when the average variable torque Tca isbalanced with the urging torque Ts at the time of limiting the actualphase Pr within the target phase range ΔPt, the oil is certainlysupplied to the advancing chambers 51-54 or the retarding chambers 55-58by alternately repeating the advancing supply period and the retardingsupply period. In this way, even under the influence of the relativelylarge variable torque, the outflow of the oil from the advancingchambers 51-54 and the retarding chambers 55-58 is well limited.Therefore, the fluctuating movement (oscillating rotational movement) ofthe vane rotor 14 relative to the housing 18 can be limited without theneed for increasing the urging torque Ts of the assist spring 22.Furthermore, the advancing supply period and the retarding supply periodare alternately repeated to generate the rotational torque Tv, whichshows the cyclic change with the period of cycle that is different fromthe period ω of cycle of the change in the variable torque. Therefore,the rotational torque Tv acts against the variable torque to effectivelylimit the fluctuating movement of the vane rotor 14.

As described above, according to the first embodiment, the actual phasePr is appropriately limited within the target phase range ΔPt, and thevalve timing is adjusted to the appropriate timing, which is appropriatefor the internal combustion engine. Furthermore, the hammering sound,which is caused by the collision between the housing 18 and the vanerotor 14, can be advantageously limited.

Second Embodiment

A second embodiment of the present invention, which is a modification ofthe first embodiment, will be described with reference to FIG. 12.

As shown in FIG. 12, the discharge pressure of the oil at the oil pump 4driven by the internal combustion engine, i.e., the pressure of the oilsupplied to the advancing chambers 51-54 and the retarding chambers55-58 is increased in response to an increase in the rotational speed ofthe internal combustion engine. Also, the pressure of the oil changesdepending on the environmental temperature.

In view of the above point, according to the second embodiment, thecontrol circuit 36 returns the actual phase Pr to an intermediate phase(a phase intermediate between the advancing end and the retarding end)in the target phase range ΔPt and then executes the alternatelyrepeating supply operation, which is similar to that of the firstembodiment, in the case where the actual phase Pr reaches the advancingend of the target phase range ΔPt, and the pressure of the oil becomesequal to or less than a preset value S during the execution of thenormal holding operation (hereinafter, simply referred to as “normalholding operation”) for substantially holding the valve timing byadjusting the drive current supplied to the switch control valve 31within the range lower than the reference value Ib. Thereby, in the lowoil pressure state where the pressure of the oil is equal to or lessthan the preset value S, it is possible to reliably limit thefluctuating movement of the vane rotor 14, which tends to occur in thelow oil pressure state.

Even in the case where the actual phase Pr reaches the advancing end ofthe target phase range ΔPt during the normal holding operation, as longas the pressure of the oil is larger than the preset value S (e.g.,about 250 kPa), the possibility of the fluctuating movement of the vanerotor 14 is reduced in comparison to the case where the pressure of theoil is equal to or less than the preset value S. Therefore, in such acase, according to the present embodiment, the normal holding operationis maintained without executing the alternately repeating supplyoperation.

Third Embodiment

A third embodiment of the present invention, which is a modification ofthe first embodiment, will be described with reference to FIGS. 13 and14. As shown in FIG. 13, the urging torque Ts of the assist spring 22increases when the relative rotational position of the vane rotor 14relative to the housing 18 is shifted in the retarding direction Y,i.e., when the engine phase of the camshaft 2 relative to the crankshaftis shifted in the retarding direction Y. Furthermore, as discussed inthe first embodiment (see FIG. 8), the average variable torque Tcincreases when the rotational speed of the internal combustion engineincreases. With reference to FIG. 14, for descriptive purpose, it is nowdefined that a reference rotational speed Nb of the internal combustionengine is a rotational speed, at which the average variable torque Tcacoincides with a minimum value Tsmin of the urging torque Ts. Then, whenthe actual rotational speed Nr of the internal combustion engine becomesequal to or higher than this reference rotational speed Nb, the averagevariable torque Tc may possibly be balanced with the urging torque Ts.

Therefore, according to the third embodiment, in the case where theactual rotational speed Nr becomes equal to or higher than the referencerotational speed Nb during the normal holding operation, the controlcircuit 36 executes the alternately repeating supply operation, which issimilar to that of the first embodiment. In this way, in the case wherethe average variable torque Tca is balanced with the urging torque Ts,it is possible to reliably limit the fluctuating movement of the vanerotor 14 by the alternately repeating supply operation.

In contrast, in the case where the actual rotational speed Nr is lessthan the reference rotational seed Nb, the average variable torque Tcais less likely balanced with the urging torque Ts. Therefore, in such acase, according to the present embodiment, the normal holding operationis maintained without executing the alternately repeating supplyoperation.

Fourth Embodiment

A fourth embodiment of the present invention, which is a modification ofthe first embodiment, will be described with reference to FIGS. 15A and15B. In the fourth embodiment, as shown in FIGS. 15A and 15B, thecontrol circuit 36 starts the alternately repeating supply operation,which is similar to that of the first embodiment, upon satisfaction ofthe stable operational condition, which serves as the limitingcondition. Then, when the stable operational condition is no longersatisfied, the control circuit 36 terminates the alternately repeatingsupply operation. Specifically, according to the present embodiment, thealternately repeating supply operation is maintained while the actualphase Pr is limited within the target phase range ΔPt upon thesatisfaction of the stable condition. Thus, according to the fourthembodiment, even when the average variable torque Tca is balanced withthe urging torque Ts of the assist spring 22, the fluctuating movementof the vane rotor 14 can be reliably limited by the alternatelyrepeating supply operation.

The present invention has been described with respect to the aboveembodiments. However, the present invention is not limited to the aboveembodiments, and the above embodiments may be modified within a spiritand scope of the present invention.

For example, a bearing may be interposed between the camshaft 2 and thejournal thereof to substantially eliminate the friction between thecamshaft 2 and the journal, and the assist spring 22 may be eliminated.Even with this construction, the fluctuating movement of the vane rotor14 can be limited by the holding operation, which maintains thealternately repeating supply operation like in the fourth embodiment.

Furthermore, in the first to fourth embodiments, the supply of the oilto the respective advancing chambers 51-54 may be intermittentlyperformed in the advancing supply period. In other words, it is notnecessary to maintain the supply of the oil to the respective advancingchambers 51-54 throughout each advancing supply period, and the supplyof the oil to the respective advancing chambers 51-54 may be stoppedbefore the end of the advancing supply period, if desired. Similarly, inthe first to fourth embodiments, the supply of the oil to the retardingchambers 55-58 may be intermittently performed in the retarding supplyperiod. In other words, it is not necessary to maintain the supply ofthe oil to the respective retarding chambers 55-58 throughout eachadvancing supply period, and the supply of the oil to the respectiveretarding chambers 55-58 may be stopped before the end of the retardingsupply period, if desired.

Furthermore, in the first embodiment, when the actual phase Pr reachesthe advancing end of the target phase range ΔPt during the normalholding operation, the alternately repeating supply operation, which issimilar to that of the first embodiment, may be started immediately fromthe beginning of the retarding supply period. Furthermore, in the secondembodiment, when the actual phase Pr reaches the advancing end of thetarget phase range ΔPt during the normal holding operation, and thepressure of the oil becomes equal to or less than the preset value S,the alternately repeating supply operation, which is similar to that ofthe first embodiment, may be started immediately from the beginning ofthe retarding supply period.

Furthermore, in the third embodiment, like in the second embodiment,when the actual rotational speed Nr of the internal combustion enginebecomes equal to or larger than the reference rotational speed Nb duringthe normal holding operation, and the pressure of the oil becomes equalto or less than the preset value S, the alternately repeating supplyoperation, which is similar to that of the first embodiment, may beexecuted. Similarly, in the fourth embodiment, the normal holdingoperation may be started upon satisfaction of the stable condition,which serves as the limiting condition. Then, when the pressure of theoil becomes equal to or less than the preset value S during the normalholding operation, the alternately repeating supply operation, which issimilar to that of the first embodiment, may be executed.

In addition, in the first to fourth embodiments, the housing 18 isrotated together with the crankshaft, and the vane rotor 14 is rotatedtogether with the camshaft 2. However, the present invention is alsoapplicable to a valve timing adjuster, in which the vane rotor 14 isrotated together with the crankshaft, and the housing 18 is rotatedtogether with the camshaft 2.

Furthermore, in the first to fourth embodiments, the present inventionis applied to the valve timing adjuster, which controls the valve timingof the exhaust valves. Alternatively, the present invention may beapplied to a system, which controls valve timing of intake valves, or asystem, which controls the valve timing of both of the intake valves andthe exhaust valves.

Additional advantages and modifications will readily occur to thoseskilled in the art. The invention in its broader terms is therefore notlimited to the specific details, representative apparatus, andillustrative examples shown and described.

1. A valve timing adjuster that adjusts opening and closing timing of atleast one of an intake valve and an exhaust valve of an internalcombustion engine and is placed in a drive force transmission system,which transmits a drive force from a drive shaft of the internalcombustion engine to a driven shaft that drives the at least one of theintake valve and the exhaust valve to open and close the same, the valvetiming adjuster comprising: a first rotatable body that is rotatedtogether with the drive shaft; a second rotatable body that is rotatedtogether with the driven shaft, wherein the second rotatable bodycooperates with the first rotatable body to form an advancing chamberand a retarding chamber, which are arranged one after another in arotational direction between the first rotatable body and the secondrotatable body, and the second rotatable body drives the driven shaft inan advancing direction or a retarding direction relative to the driveshaft upon supplying of working fluid to the advancing chamber or theretarding chamber; and a supply control means for controlling supply ofthe working fluid to the advancing chamber and the retarding chamber,wherein the supply control means alternately and repeatedly implementsan advancing supply period, during which the working fluid is suppliedto the advancing chamber, and a retarding supply period, during whichthe working fluid is supplied to the retarding chamber, at time oflimiting a phase of the driven shaft relative to the drive shaft withina target phase range.
 2. The valve timing adjuster according to claim 1,further comprising a resilient member that generates an urging torque tourge the driven shaft in a direction that is opposite from a directionof an average torque of a variable torque, which changes with time andis applied to the driven shaft.
 3. The valve timing adjuster accordingto claim 2, wherein the supply control means alternately and repeatedlyimplements the advancing supply period and the retarding supply periodin a case where an actual phase of the driven shaft relative to thedrive shaft reaches a corresponding one of an advancing end and aretarding end of the target phase range, which is opposite from thedirection of the average torque upon satisfaction of a limitingcondition for limiting the phase of the driven shaft relative to thedrive shaft within the target phase range.
 4. The valve timing adjusteraccording to claim 3, wherein the supply control means alternately andrepeatedly implements the advancing supply period and the retardingsupply period after the supply control means returns the actual phase toan intermediate phase in the target phase range in the case where theactual phase reaches the corresponding one of the advancing end and theretarding end of the target phase range, which is opposite from thedirection of the average torque, upon the satisfaction of the limitingcondition for limiting the phase of the driven shaft relative to thedrive shaft within the target phase range.
 5. The valve timing adjusteraccording to claim 2, wherein: the supply control means alternately andrepeatedly implements the advancing supply period and the retardingsupply period in a case where an actual rotational speed of the internalcombustion engine becomes equal to or larger than a reference rotationalspeed of the internal combustion engine upon satisfaction of a limitingcondition for limiting the phase of the driven shaft relative to thedrive shaft within the target phase range; and the reference rotationalspeed of the internal combustion engine is defined as a rotational speedof the internal combustion engine, at which the average torque thatincreases as the rotational speed of the internal combustion engineincreases generally coincides with a minimum value of the urging torque.6. The valve timing adjuster according to claim 1, wherein the supplycontrol means maintains the alternately and repeatedly implementing ofthe advancing supply period and the retarding supply period as long asthe supply control means limits the phase of the driven shaft relativeto the drive shaft within the target phase range.
 7. The valve timingadjuster according to claim 1, wherein: a rotational torque, whichdrives the driven shaft in an advancing direction or a retardingdirection relative to the drive shaft, is generated by the supplying ofthe working fluid to the advancing chamber or the retarding chamber; andthe supply control means alternately and repeatedly implements theadvancing supply period and the retarding supply period such that therotational torque is generated with a different period of a cycle thatis different from a period of a cycle of the variable torque.
 8. Thevalve timing adjuster according to claim 1, wherein: a rotationaltorque, which drives the driven shaft in an advancing direction or aretarding direction relative to the drive shaft, is generated by thesupplying of the working fluid to the advancing chamber or the retardingchamber; and the supply control means alternately and repeatedlyimplements the advancing supply period and the retarding supply periodin a case where a pressure of the working fluid supplied to theadvancing chamber and the retarding chamber becomes equal to or lessthan a preset value upon satisfaction of a limiting condition forlimiting the phase of the driven shaft relative to the drive shaftwithin a target phase range.